Building a Tunnel

[hyphagon]

Hi All,

I am in the middle of digging out ready to build a tunnel. The plan is to have a concrete bed 4" thick with concrete paving slabs (400 x 400 mm cut to size) as the sides and top. I`ve attached a pdf with a drawing as it worth a thousand words!! The side slabs I was planning on sinking 2" into the concrete and allow them to set in place.

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I was just wondering if anyone has built something similar and if this will be strong enough. Or if there is a better idea!

Thanks

Dan

 

[a98087]

I've done very a similar idea to you except I used bricks for the side walls, and a cut down 3x2 paving slab for the foundation and tunnel roof as it was quicker than casting my own, and it's a short tunnel.


I personally wouldn't use patio slabs for walls as if the ground were to move over time, then tunnel would be come an interesting shape quite quickly,

if you were to widen the tunnel slightly and use bricks (normal or breeze) then it would be nice and strong and last a very long time,

There's some pictures in my picture thread I think

Dan

 

[owlpool]

similar plan with mine, though not completed yet
I cut an over-wide trench, poured a base around reinforcing and will be building brick sides with pebbles behind for drainage. slabs and an inspection plate on top

http://www.gscalecentral.net/track-track-laying/pdr-highland-extension-up-and-running/

pics 112, 113, 114

 

[Wobbleboxer]

How long is it going to be and what's going on top? They will be determining factors in terms of strength and don't forget to buy some longer arms or include an access point (like Owlpool)

 

[French Chuffed]

I was looking through my old pictures this was my tunnel and it stood the test of time.

 

[minimans]

I built mine from 2X12 pressure treated lumber it`s been there for 10 odd years covered in 3 ft of dirt and it`s still solid as a rock.............................

 

[hyphagon]

Thanks for the replies especially the photo`s.

New plans have been drawn up using concrete blocks! I`ve been in the garden widening the tunnel this morning ready to pour the concrete later. It does seem silly not to take a little extra time using blocks as even if it is over engineered its not worth the risk of a collapse in years to come. I think I will still use the slabs to cover the top as there is only minimal soil going on top and they should easily be adequate.

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Wobbleboxer the tunnel is going to be around 5-6m long (escape points have been planned). Also curving and going on a gradient! I am building a loop and the tunnel will start on the bottom track where the top overlaps until it pops out the ground a point which has yet to been decided!

Owlpool your comment about pebbles got me thinking about drainage. I was planning on having weep holes at the base of every other block (top of the concrete) to let water out of the tunnel BUT if I put pebbles on the outside of the tunnel will that encourage water to flow the opposite way through the weep holes into the tunnel?

Minimans I like you timber tunnel. I did consider timber but unfortunately I couldn`t keep the costs down and seeing as its underground I will rarely see it. Although one entrance is though old creosoted sleepers.

 

[owlpool]

progress!
my tunnel is on a gradient too, so drainage from the trackbed is sorted
I wasn't going to have weep holes for the reason you outline, but the ground seepage from around the tunnel has to have somewhere to go, hence the pebbles

 

[minimans]

Minimans I like you timber tunnel. I did consider timber but unfortunately I couldn't keep the costs down and seeing as its underground I will rarely see it. Although one entrance is though old creosoted sleepers.

Oh! A gradient on a curve? I think you will be seeing the inside of that tunnel more than you think mate! Murphy's law has a big impact on tunnels you know..................